1. Field of the Invention
The present invention relates to optical digital equipment for digitally processing an optical signal bearing digital information.
2. Related Background Art
In digital electronic technology represented by an electronic computer, a digital optical technique in which light is used to replace electrons as an electronic transmission medium to attain a high speed operation has been attracting much attention. In the field of the digital optical technique, a current target is directed at a digital optical computer and various systems and apparatus have been proposed and tested for an optical digital processor which is a base of the configuration.
A first example of such a processor is an optical digital apparatus using a space coded operation method represented by OPALS (Optical Parallel Array Logic System): J. Tanida et al, Applied Optics 25 (20), May 1986, pages 1565-1570). In this operation method, "0" and "1" information coded in a first direction of a space to a first optical signal to be operated and "0" and "1" information coded in a second direction normal to the first direction of the space to a second optical signal to be operated are superimposed to form a planar mask pattern. Then, lights are emitted from a plurality of light sources arranged in a space in a third direction normal to the first and second directions and an operation result is reflected to a specified area of an combined image of the lights through the mask pattern.
A second example is an optical digital apparatus which uses a holographic look-up table method (C. C. Guest et al., Applied Optics 23 (19), October 1984, pages 3444-3454). In this method, results corresponding to all combinations of input signal values for a predetermined operation to predetermined input signals are recorded in a hologram. In executing the operation, a coherent light corresponding to the input signal value is irradiated to the hologram and an operation result for the input signal value in the execution of the operation is derived from the reproduced image. In this method, any operation may be executed without regard to the complexity and the number of inputs and the operation time is substantially constant without regard to the time required to prepare the hologram. In addition, the operation time can be sufficiently short.
A third example is an optical gate logic device which uses a non-linear device having a non-linear optical effect. In this device, a sum of a plurality of lights is applied to a non-linear device and an interactive light emitted from the non-linear device by the non-linear optical effect is used as an operation result. In principle, a plurality of such devices may be combined.